Cement Kiln Exhaust Gas Pollution Reduction

ABSTRACT

A method for reducing pollution in a cement kiln environment and a system for treating cement kiln exhaust gas are provided. The method includes the steps of: treating a cement kiln exhaust gas stream with a treating fluid, such as a water soluble alkaline-earth metal sulfide. In one application, the treating fluid is injected by spraying droplets into the cement kiln exhaust gas stream. A system for treating cement kiln exhaust gas includes a reagent containing a water soluble alkaline-earth metal sulfide in water, and a nozzle to spray the reagent into the cement kiln exhaust gas stream.

FIELD

The present disclosure relates to heavy-metal pollution reduction in thecement kiln environment.

BACKGROUND

Cement kiln exhaust gases vary significantly and typically containvolatile heavy metals, such as mercury, which are generally volatilizedfrom the raw materials and fuels during the clinkering process, andcarried into the atmosphere. Cement kiln exhaust gases typically containoxides of carbon, sulfur, nitrogen, alkalis, excess chlorides andvolatile heavy metals such as mercury. Mercury in both its elemental andionic form are generally continually emitted through the cement kilnexhaust stack in varying concentrations dependent upon the operation ofthe kiln, in-line raw mill and raw material or fuel inputs.

These gases may also be re-used for drying and heating within the inlineraw mill and then exit the process as cement kiln exhaust gas. The heavymetals within the gases may then be released to the atmosphere afterthey pass through a kiln baghouse electrostatic precipitator, or otherparticulate collection apparatus.

Typical mercury concentrations in cement kiln exhaust gases may varysignificantly and are highly dependent on the raw materials, processconditions, and fuels burned in the clinkering process at each site.Previous attempts to capture and contain mercury from cement kilnexhaust gas in both its elemental and its oxide form have generally hadmixed results. These processes may also be expensive. These processesinclude activated carbon injection, flue gas desulphurization scrubbers,and sorbent technology. These processes do not generally render theresidual mercury in a stable, non-leachable form which can be used as aprocess addition while having no detrimental effects on the resultingportland cement or concrete.

Treatment processes for power plants such as those disclosed in HurleyU.S. Pat. Nos. 7,407,602, 7,771,683, and 7,776,294 are likewiseinapplicable or inappropriate to the environment of the cement kiln fora variety of reasons.

SUMMARY

In an illustrative embodiment, a method for treating cement kiln exhaustgas is disclosed. The method includes providing a cement kiln exhaustgas stream from a kiln; providing a reagent containing a water solublealkaline-earth metal polysulfide; combining the cement kiln exhauststream with the reagent to create a combined stream; and removing atleast a portion of one heavy metal, such as mercury, from the combinedstream. The method may further include passing the combined streamthrough a particulate collection system and recycling the collectedparticulate for use as raw material in the kiln.

In combining the cement kiln exhaust stream with the reagent, the methodmay include spraying the reagent into the cement kiln exhaust stream.The method may include combining the reagent with water prior tocombining the cement kiln exhaust stream with the reagent. The ratio ofreagent to water may vary significantly from cement kiln to cement kiln.Factors affecting the amount of reagent used or its ratio to water mayinclude the kiln exhaust's particulate load, dispersion, exhaust gasvelocity, presence and amount of metals other than mercury, and anynumber of other environmental or processing parameters. It is oftendesirable to use as little of the reagent as needed to achieve thedesired amount of mercury reduction. In one set of cement kilnapplications, the reagent and the water may be combined in ratiosranging from about 1:3 to about 1:6.

The method may also include providing at least one of a surfactant, adispersant, and a hyperdispersant, and combining the reagent and waterwith the at least one of the surfactant, the dispersant, and thehyperdispersant prior to combining the cement kiln exhaust stream withthe reagent.

The reagent containing the water soluble alkaline-earth metalpolysulfide may include the water soluble alkaline-earth metalpolysulfide in a concentration of about 20% to about 40% in water, andmore particularly in a concentration of about 30% in water.

In an illustrative embodiment, a method for reducing pollution in acement kiln environment is disclosed. In this embodiment, the methodincludes treating a cement kiln exhaust gas stream with a treating fluidcomprising a reagent containing a water soluble alkaline-earth metalpolysulfide by injecting the treating fluid into the cement kiln exhaustgas stream prior to a particulate collection system.

Injecting the treating fluid, may include spraying droplets of thetreating fluid into the cement kiln exhaust gas stream. The treatingfluid may be injected into the cement kiln exhaust gas stream at a pointwhere the cement kiln exhaust gas stream has a temperature of about 350degrees Fahrenheit. The treating fluid may be injected into the cementkiln exhaust gas stream subsequent to a first particulate collectionsystem and prior to a second particulate collection system. The treatingfluid may also be injected into a gas resonance chamber or a ductcarrying the cement kiln exhaust gas stream.

The treating fluid may also contain water and at least one of asurfactant and a hyperdispersant. The system and method may be adaptedso that the droplets have a size which allows the droplets to have aminimum residence time of about 1 to about 2 seconds within the cementkiln exhaust stream. In some applications, this minimum residence timemay be achieved when the droplets have an average size of about 20microns or greater, and more particularly about 30 microns to about 40microns. Longer residence times are likewise both achievable andsuitable for cement kiln applications, as are larger droplet sizes.

In an illustrative embodiment, a system for treating cement kiln exhaustgas is disclosed. The system includes a treating fluid; at least onenozzle configured to communicate with a cement kiln exhaust gas streamfrom a kiln and to spray droplets of the treating fluid into the cementkiln exhaust gas stream; and at least one vessel fluidly connected tothe nozzle and configured to store the treating fluid.

The nozzle may be configured to spray droplets having a size configuredto allow the droplets to have a minimum residence time of about 1 toabout 4 seconds. The nozzle may be configured to spray droplets havingan average size of about 20 microns or greater.

The treating fluid may comprise a reagent containing a water solublealkaline-earth metal polysulfide in water. The treating fluid mayinclude the reagent combined with water. The treating fluid may alsoinclude at least one of a surfactant, a dispersant, and ahyperdispersant.

The treating fluid may consist essentially of a reagent containing awater soluble alkaline-earth metal sulfide and/or polysulfide. Thetreating fluid may consist essentially of water and a reagent containinga water soluble alkaline-earth metal sulfide and/or polysulfide. Thetreating fluid may consist essentially of a reagent containing a watersoluble alkaline-earth metal sulfide and/or polysulfide, and at leastone of a surfactant, a dispersant, and a hyperdispersant.

The treating fluid may consist of a reagent containing a water solublealkaline-earth metal sulfide and/or polysulfide. The treating fluid mayconsist of water and a reagent containing a water soluble alkaline-earthmetal sulfide and/or polysulfide. The treating fluid may consist of areagent containing a water soluble alkaline-earth metal sulfide and/orpolysulfide, and at least one of a surfactant, a dispersant, and ahyperdispersant.

In an illustrative embodiment, the treating fluid reacts with mercurywithin the cement kiln exhaust gas stream to form mercury sulfide. Themercury sulfide may no longer be soluble in terms of leachate in soils,cement or concrete as the captured mercury and other metals are nowinsoluble. The resulting particulates can be collected by a particulatecollection system and transferred to storage for controlled meteringback into a cement grinding mill and/or used as a filler material withina concrete batch plant, asphalt plant or landfilled.

Utilization of the systems and methods disclosed herein in theapplication of a cement kiln gas resonance chamber prior to the existingkiln baghouse or electrostatic precipitator may reduce investment costand operating cost when contrasted with a wet scrubber, dry scrubberapplication or activated carbon injection.

In an illustrative embodiment, the application of an integrated ductsystem prior to an existing kiln baghouse or electrostatic precipitatormay reduce investment cost and operating cost when contrasted with a wetscrubber, dry scrubber application or activated carbon injection. Theapplication of the integrated duct system or gas resonance chamber afterthe existing kiln baghouse or electrostatic precipitator may reduceoperating cost when contrasted with activated carbon injection.

These and other aspects of the disclosure may be understood more readilyfrom the following description and the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the disclosure are illustrated in the figures of theaccompanying drawings which are meant to be exemplary and not limiting,in which like references are intended to refer to like or correspondingparts, and in which:

FIG. 1 illustrates an embodiment of a system and method for treatingcement kiln exhaust gases to reduce pollution where the treating fluidis sprayed into a duct containing cement kiln dust;

FIG. 2 illustrates an embodiment of a system and method for treatingcement kiln exhaust gases to reduce pollution where the treating fluidis sprayed into a gas resonance chamber, cyclone, or additional ductcontaining cement kiln dust;

FIG. 3 illustrates an embodiment of a system and method for treatingcement kiln exhaust gases to reduce pollution where the treating fluidis sprayed into a gas resonance chamber, cyclone, or additional ductbetween two particulate collection systems;

FIG. 4 illustrates an embodiment of a method of recycling modifiedcement kiln dust and other raw materials;

FIG. 5 illustrates an embodiment of an integrated injection system andmethod for treating cement kiln exhaust gases to reduce pollution;

FIG. 6 illustrates an enlarged view of one portion of the system of FIG.5 including two injection points;

FIG. 7 illustrates a top sectional view of the two injection points ofFIG. 6;

FIG. 8 illustrates an embodiment of a lance suitable for use in thevarious embodiments of this disclosure, including the systems of FIGS.5-7;

FIG. 9 illustrates a schematic view of an embodiment of a spray patternfrom the nozzles at one injection point of the system of FIGS. 5-8;

FIG. 10 illustrates an embodiment of fluid connections at the injectionpoint of the system of FIG. 9;

FIG. 11 illustrates a schematic view of an embodiment of a spray patternthrough the nozzles at another injection point of the system of FIGS.5-8;

FIG. 12 illustrates an embodiment of fluid connections the injectionpoint of the system of FIG. 11; and

FIG. 13 illustrates a table of data collected through the use of theintegrated injection system and method of FIGS. 5-12 for treating cementkiln exhaust gases to reduce pollution.

DETAILED DESCRIPTION

Detailed embodiments of the systems, methods, and apparatuses for cementkiln exhaust gas pollution reduction are disclosed herein; however, itis to be understood that the disclosed embodiments are merely exemplaryof the systems, methods, and apparatuses, which may be embodied invarious forms. Therefore, specific functional details disclosed hereinare not to be interpreted as limiting, but merely as a basis for theclaims and as a representative basis for teaching one skilled in the artto variously employ the systems, methods, and apparatuses for cementkiln exhaust gas pollution reduction.

The heavy metals, such as mercury, which are sought to be managedthrough the systems, methods, and apparatuses of the present disclosureare derived primarily from raw materials which are chemically alteredduring a clinker process releasing these materials into a cement kilnexhaust gas stream containing cement kiln dust, and to the atmospherethrough a kiln baghouse, electrostatic precipitator (ESP), or otherparticulate collection system. These raw materials may include calcium,silica, iron and alumina derived primarily from various forms oflimestone, clay, shale, slags, sand, mill scale, iron-rich material(IRM), pumice, bauxite, recycled glass, ashes, and similar materials.

In one illustrative embodiment, cement kiln exhaust gases are typicallypassed from a kiln through one or more processes, ducts, mills,cyclones, particulate collection systems such as kiln bag houses, ESPs,or other particulate collection systems, and exit at a kiln exhauststack. As illustrated in FIGS. 1-3, the cement kiln exhaust gas stream22 containing cement kiln dust is passed from a kiln (not shown) to anexhaust gas diverter gate 24. At the diverter gate 24, all or a portionof the cement kiln exhaust gas stream 22 may be passed through a duct 26and used for drying and heating within a raw mill 28, or passed througha bypass duct 30. As illustrated in FIGS. 1-3, when all or a portion ofthe cement kiln exhaust gas stream 22 is used for drying and heatingwithin the raw mill 28, the cement kiln exhaust gas stream 22 passesthrough the raw mill 28 and a duct 32 to a raw mill cyclone or cyclone34 located above a kiln feed silo 36. After the cement kiln exhaust gasstream 22 passes through the cyclone 34, the cement kiln exhaust gasstream 22 passes through a return duct 38, which connects with thebypass duct 30.

The cement kiln exhaust gas stream 22 in the bypass duct 30 may thenpass through one or more particulate collection systems 40 during whichparticulates may be collected and used as a modified cement kiln dust(mCKD) 42. After the particulate collection system(s) 40, the cementkiln exhaust gas stream 22 passes through a duct 44 and exits through akiln exhaust stack 46.

In an illustrative embodiment, the cement kiln exhaust gas stream 22 istreated with a fluid, solution, or treating fluid, by injecting orspraying the treating fluid into one or more ducts, chambers, or otherprocess equipment carrying the cement kiln exhaust gas stream 22. Thetreating fluid may be provided in a fully soluble form enabling low costapplication and retrofitting of existing facilities.

The treating fluid may contain a reagent containing an alkaline-earthmetal sulfide and/or polysulfide. The alkaline-earth metal sulfideand/or polysulfide may have a pH of about 10 or more, and the treatingfluid may have a pH of about 7 to 10 dependent upon the concentration ofreagent in the treating fluid. In one embodiment, the reagent maycontain the alkaline-earth metal sulfide and/or polysulfide typically ata concentration of about 20% to 40% in water. In another embodiment, thereagent may contain the alkaline-earth metal sulfide and/or polysulfideat higher concentrations in water, or, alternately, may be in a powderor solid form having a substantially higher percentage, or consistingentirely, of the alkaline-earth metal sulfide and/or polysulfide. Thealkaline-earth metal sulfide/polysulfide may be added to another solid,powder, or liquid carrier to form the reagent.

In an illustrative embodiment, the reagent contains an alkaline-earthmetal polysulfide in water. The alkaline-earth metal polysulfide may beeither a magnesium or calcium polysulfide, and may be present in thereagent in an amount of about 25% to 35%, or about 25% to 30% in water.In another illustrative embodiment, the alkaline-earth metal polysulfideis a mixture of magnesium polysulfides and calcium polysulfides, whereinthe polysulfides are present in the reagent in an amount of about 25% to35%, or about 25% to 30% in water.

In an illustrative embodiment, the treating fluid contains the reagentand water. The treating fluid may contain the reagent and water in aratio of about 1:1 to 1:10, in a ratio of about 1:3 to 1:6, and moreparticularly in a ratio of about 1:4. When the reagent contains thealkaline-earth metal sulfide and/or polysulfide at a concentration ofabout 20% to 40% in water, the resulting treating fluid may contain thealkaline-earth metal sulfide and/or polysulfide and water in ratios ofabout 1:4 to about 1:54, in a ratio of about 1:9 to 1:34, and moreparticularly in a ratio of about 1:11 to 1:24. Thus, the alkaline-earthmetal sulfide and/or polysulfide may be present in the treating solutionin an amount of about 1.8% to 11%. However, it should be appreciatedthat the ratios of reagent to water and/or the alkaline-earth metalsulfide and/or polysulfide to water can vary outside of the rangeslisted above. In many applications, the economic goal may be to use aslittle of the reagent and/or the alkaline-earth metal sulfide and/orpolysulfide as operationally possible. For example, the ratios used canvary dependent upon the particulate load and dispersion in the cementkiln exhaust gas stream, the exhaust gas stream velocity, theconcentration of mercury and other metals in the cement kiln exhaust gasstream, and other parameters of the type.

The reagent and water may be combined into the treating fluid prior toinjecting or spraying the treating fluid into the one or more ducts,chambers, or other process equipment carrying the cement kiln exhaustgas stream 22. For example, the reagent and water may be combined wellin advance of (i.e. one or more hours, days, weeks, months, etc. inadvance) or just prior to (i.e. one or more minutes prior to) injectingor spraying the treating fluid into the one or more ducts, chambers, orother process equipment.

Alternatively, the reagent and water may each be separately sprayed orinjected into the one or more ducts, chambers, or other processequipment carrying the cement kiln exhaust gas stream 22 in a mannersuch that they intersect, combine, interact or coalesce in the one ormore ducts, chambers, or other process equipment to form a solution orcomposition in situ, forming droplets of the solution or compositionwith the reagent reacting with the metal(s) in the cement kiln exhaustgas stream 22 for removal. In another variation, the treating fluid maybe introduced to the cement kiln exhaust gas stream 22 by adding it to aconventional flue gas desulfurization solution that is sprayed into aduct.

The treating fluid may also contain one or more surfactants,dispersants, and/or hyperdispersants to assist in the removal ofmetal(s) from the cement kiln exhaust gas stream 22. In one embodiment,the surfactant, dispersant, and/or hyperdispersant is composed of one ormore polyethylene oxide-polyethylene block co-polymers and/or thephosphate esters thereof. The addition of the surfactant, dispersant,and/or hyper dispersant to the treating fluid may be optional. When thesurfactant, dispersant, and/or hyper dispersant is included, thesurfactant, dispersant, and/or hyper dispersant may be provided in anamount sufficient to assist in maintaining the reaction agent or reagentin the treating fluid prior to reaction with the metal(s), for examplein an amount of about 1% or less. According to the latter case, thesurfactant, dispersant, and/or hyper dispersant is a polyethyleneoxide-polyethylene block co-polymer and the phosphate esters thereof.

In an illustrative embodiment, the reagent, water, and the one or moresurfactants, dispersants, and/or hyper dispersants may be combined intothe treating fluid prior to injecting or spraying the treating fluidinto the one or more ducts, chambers, or other process equipmentcarrying the cement kiln exhaust gas stream 22. For example, thereagent, water, and the one or more surfactants, dispersants, and/orhyper dispersants may be combined well in advance of (i.e. one or morehours, days, weeks, months, etc. in advance) or just prior to (i.e. oneor more minutes prior to) injecting or spraying the treating fluid intothe one or more ducts, chambers, or other process equipment.

In an illustrative embodiment, the treating fluid is sprayed or injectedinto the cement kiln exhaust gas stream 22. The treating fluid may besprayed or injected into the cement kiln exhaust gas stream 22 through agas resonance chamber or integrated into suitable ductwork prior to orafter the cement kiln baghouse, electrostatic precipitator, orparticulate collection system 40, and/or a flue gas desulfurizationscrubber. The gas resonance chamber or ductwork is configured to form azone which assists in bringing the particulate and the gas stream in thecement kiln exhaust gas stream 22 into contact with, and reacting with,the treating fluid. The treating fluid reacts with the gas laden withmetals and cement kiln dust to form a particulate residue of the metalson and within the cement kiln dust (CKD). In one embodiment, thetreating fluid reacts with mercury within the cement kiln exhaust gasstream 22 to form mercury sulfide.

Once the cement kiln exhaust gas stream 22 in the chamber or ductwork isacted upon by the treating fluid, the particulate residue is generallycaptured downstream, which, depending on the particular configuration,may be within the existing kiln baghouse, electrostatic precipitator, ina secondary polishing baghouse, or other particulate collection system40. The captured particulate is typically a dry material referred to asmodified cement kiln dust (mCKD). In the case of a cement kiln equippedwith a flue gas desulfurization scrubber, a particulate residue may alsobe captured within the scrubber as a component of the generatedsynthetic gypsum resulting in modified synthetic gypsum (mSyngyp). ThemCKD and/or the mSyngyp can then be transferred to storage forcontrolled metering back into a cement grinding mill and/or used as afiller material within a concrete batch plant, asphalt plant orlandfilled as non-leachable mCKD and mSyngyp.

In an illustrative embodiment, the spray or injection timing of thetreating fluid into the cement kiln exhaust gas stream 22 may be alignedwith the operation of the raw mill 28, may be continuous, or may beintermittent, dependent upon the needs of the plant. In certainapplications, the system for injecting the fluid (also referred toherein as the injection system) is operated when the exhaust is morelikely to exceed applicable emission limits for the heavy metals beingcaptured. For example, in certain applications, when the raw mill 28 isnot operating, the exhaust gas may be more likely to include higherconcentrations of heavy metals, and the injection system may be operatedsuitably at that time. Other cement kiln operations may require theinjection system to operate while the raw mill 28 is also operating,depending on the cement making apparatus and process with which theinjection system is associated, as well as the location of suchinjection system.

In an illustrative embodiment, the injection system for treating cementkiln exhaust gases includes a tank or other suitable vessel for storingthe spray or treating fluid, and suitable fluid connections to thecement kiln exhaust gas stream to transport the fluid into operativeproximity to the cement kiln exhaust gas stream containing mercury andother metals to be captured. The injection system includes one or morenozzles, ports, or other suitable openings positioned so that a sprayfluid is formed. Multiple nozzles at spaced locations and with differingangular orientations generate a suitable dispersal pattern to contactthe cement kiln exhaust gas stream.

A system and method for treating cement kiln exhaust gases to reducepollution according to an illustrative embodiment is described withreference to FIG. 1. As illustrated in FIG. 1, the injection systemincludes one or more nozzles 48 integrated into the ductwork used totransport the cement kiln exhaust gas stream 22 from the kiln (notshown). In this illustrative embodiment, the nozzles 48 are integratedinto a pre-existing duct. The nozzles 48 are suitably positioned tocommunicate with bypass duct 30. The nozzles 48 are connected to avessel 50, for storing the spray or treating fluid, through one or morefluid connections 52, such as pipes and/or hoses. The treating fluid maybe stored in the vessel 50 and transported through the fluid connections52 to the cement kiln exhaust gas stream 22 in the bypass duct 30. Thetreating fluid can then be sprayed or injected into the exhaust gasstream 22.

In this embodiment, the nozzles 48 are positioned to communicate withbypass duct 30 downstream of the raw mill 28 and prior to theparticulate collection system 40. Treatment by the injection system,illustrated in FIG. 1, occurs prior to the cement kiln exhaust gasstream 22 entering the one or more particulate collection systems 40. Assuch, the injection system may be designed such that the inlettemperature of the duct system is hot enough to accommodate thetemperature drop across the injection system while in operation, whilealso meeting the operational requirements of the existing particulatecollection system 40, baghouse, or ESP, such as an inlet temperatureselected to avoid both high heat situations (for example above 400° F.)and low dew point situations (for example below 200° F.) which can leadto corrosion. It should be appreciated that the temperature drop acrossthe injection system while in operation may depend on the inlettemperature, the amount of treating fluid being injected and othervariables of the type.

In an illustrative embodiment, the treating fluid injected or sprayedthrough the nozzles 48 has a large enough droplet size allowing thetreating fluid to intercept the cement kiln exhaust gas stream for aminimum of about 1-2 seconds either intermittently or on a continualbasis while the treating fluid is being injected and the reactionoccurs. However, it should be appreciated that longer residence times orinterception times can be used and may be preferred based upon theparticular application.

Treatment by the injection system, illustrated in FIG. 1, occurs priorto the cement kiln exhaust gas stream 22 entering the one or moreparticulate collection systems 40. As such, particulates are captured asa dry residual material resulting in the modified cement kiln dust(mCKD) 42. This mCKD 42 may no longer be soluble in terms of leachate insoils, cement or concrete as the captured mercury and other metals arenow permanently insoluble. The mCKD 42 may be used as one of theadditional materials inserted into a finish mill in the cement-makingprocess, which is described in further detail below with reference toFIG. 4.

While, the injection system including nozzles 48 is integrated orinstalled in a preexisting duct, i.e. bypass duct 30, it should beappreciated that the injection system including nozzles 48 can beinstalled in one or more newly added, modified, or preexisting ducts atany number of different locations. For example, the injection system maybe installed or placed to contact the cement kiln exhaust gas stream 22upstream of the raw mill 28, downstream of the raw mill 28, in thebypass duct 30, in the return duct 38, downstream of the particulatecollection system 40, upstream of the particulate collection system 40,or in one or more existing, modified, or additional ducts associatedtherewith.

When an injection system, similar to the integrated injection systemillustrated in FIG. 1 is integrated or installed after, or downstreamof, the particulate collection system 40, kiln baghouse or ESP, theinjection system may be designed such that the inlet temperature of theinjection zone is hot enough to accommodate the temperature drop acrossthe injection zone while in operation while meeting the requirements ofa secondary particulate collection system, such as illustrated in FIG.3. This integrated injection system may be configured to spray dropletshaving a large enough droplet size to allow the droplets to interceptthe cement kiln exhaust gas stream for about 1-2 seconds or longer,either intermittently or on a continual basis while the treating fluidis being injected and the reaction occurs. The resulting particulate maybe carried directly into the secondary particulate collection system andcontained as a concentrated residue. This residue may no longer besoluble in terms of leachate in soils, cement or concrete as thecaptured mercury and other metals are now permanently insoluble.

The ductwork associated with the injection system may be pre-existing ornewly installed as part of the injection system. The ductwork associatedwith the injection system, whether pre-existing or new, may optionallybe treated with a polymer or may require additional ducting, chambers,or other modifications to its geometry to insure the treating fluid orchemical remains in an active form for a length of time suitable totreat the cement kiln exhaust gas stream as intended before entering theparticulate collection system.

In other embodiments, additional ductwork, chambers (such as gasresonance chambers), and/or modifications to the pre-existing ductworkmay be used in creating a suitable treatment or injection system.Another system and method for treating cement kiln exhaust gases toreduce pollution according to an illustrative embodiment is describedwith reference to FIG. 2. As illustrated in FIG. 2, the injection systemincludes additional duct work and is installed or placed upstream of theparticulate collection system 40. The additional ductwork includes afirst duct 54, a resonance chamber or a cyclone 56, and a second duct58. In this illustrative embodiment, the first duct 54 is connected tothe bypass duct 30, the resonance chamber 56 is connected to the firstduct 54, and the second duct 58 is connected to the resonance chamber 56and to the inlet of the particulate collection system 40. Thus, thecement kiln exhaust gas stream 22 flows from the bypass duct 30 throughthe first duct 54, through the resonance chamber 56, and through thesecond duct 58 into the particulate collection system 40.

In addition to the additional ductwork, the injection system includesone or more nozzles 60 suitably positioned to communicate with theresonance chamber 56. In this illustrative embodiment, the nozzles 60are connected to a vessel 62 for storing the spray or treating fluidthrough one or more fluid connections 64, such as pipes and/or hoses.The treating fluid it typically stored in the vessel 62 and transportedthrough the fluid connections 64 to the cement kiln exhaust gas stream22 in the resonance chamber 56. The treating fluid can then be sprayedor injected into the cement kiln exhaust gas stream 22.

In this embodiment, the nozzles 60 are positioned to communicate withresonance chamber 56 downstream of the raw mill 28 and prior to theparticulate collection system 40. Treatment by the injection system,illustrated in FIG. 2, occurs prior to the cement kiln exhaust gasstream 22 entering the one or more particulate collection systems 40.Again, in this embodiment, the injection system may be designed suchthat the inlet temperature of the resonance chamber 56 is hot enough toaccommodate the temperature drop across the resonance chamber 56 whilein operation, while also meeting the operational requirements of theexisting particulate collection system 40, baghouse, or ESP, such as aninlet temperature selected to avoid both high heat situations (forexample above 400° F.) and low dew point situations (for example below200° F.) which can lead to corrosion.

In an illustrative embodiment, the treating fluid injected or sprayedthrough the nozzles 60 has a large enough droplet size to allow thetreating fluid to intercept the cement kiln exhaust gas stream for about1-4 seconds or longer, either intermittently or on a continual basiswhile the reagents are being injected and the reaction occurs. However,it should be appreciated that longer residence times or interceptiontimes can be used and may be preferred based upon the particularapplication. As in the previous embodiments, particulates are capturedas a dry residual material resulting in the modified cement kiln dust(mCKD) 42. The mCKD 42 may be used as one of the additional materialsinserted into a finish mill in the cement-making process, which isdescribed in further detail below with reference to FIG. 4.

Another system and method for treating cement kiln exhaust gases toreduce pollution according to an illustrative embodiment is describedwith reference to FIG. 3. As illustrated in FIG. 3, the injection systemincludes additional duct work and is installed or placed between twoparticulate collection systems 40 a and 40 b. The additional ductworkincludes a first duct 66, a gas resonance chamber or a cyclone 68, and asecond duct 70. In this illustrative embodiment, the first duct 66 isconnected to the outlet of the particulate collection system 40 a, theresonance chamber 68 is connected to the first duct 66, and the secondduct 70 is connected to the resonance chamber 68 and to the inlet of theparticulate collection system 40 b. Thus, the cement kiln exhaust gasstream 22 flows from the particulate collection system 40 a through thefirst duct 66, through the resonance chamber 68, and through the secondduct 70 into the particulate collection system 40 b.

As in the previous embodiments, the injection system includes one ormore nozzles 72 suitably positioned to communicate with the resonancechamber 68. In this illustrative embodiment, the nozzles 72 areconnected to a vessel 74 for storing the spray or treating fluid throughone or more fluid connections 76, such as pipes and/or hoses. Thetreating fluid it typically stored in the vessel 74 and transportedthrough the fluid connections 76 to the cement kiln exhaust gas stream22 in the resonance chamber 68. The treating fluid can then be sprayedor injected into the exhaust gas stream 22.

In this embodiment, the nozzles 72 are positioned to communicate withthe resonance chamber 68 downstream of the particulate collection system40 a and prior to the particulate collection system 40 b. Treatment bythe injection system, illustrated in FIG. 3, occurs after theparticulate collection system 40 a and prior to the particulatecollection system 40 b. In this embodiment, similar to the others, theinjection system may be designed such that the inlet temperature of theresonance chamber 68 is hot enough to accommodate the temperature dropacross the resonance chamber 68 while in operation, while also meetingthe operational requirements of the particulate collection system 40 b,baghouse, or ESP, such as an inlet temperature selected to avoid bothhigh heat situations (for example above 400° F.) and low dew pointsituations (for example below 200° F.) which can lead to corrosion.

In this illustrative embodiment, similar to the others, the treatingfluid injected or sprayed through the nozzles 72 has a large enoughdroplet size to allow the treating fluid to intercept the cement kilnexhaust gas stream for a minimum of about 1-4 seconds, eitherintermittently or on a continual basis while the reagents are beinginjected and the reaction occurs. However, it should be appreciated thatlonger residence times or interception times can be used and may bepreferred based upon the particular application.

The resulting particulate may be carried directly into the particulatecollection system 40 b and contained as a concentrated residue 78. Thisresidue 78 may no longer be a threat in terms of leachate in soils,cement or concrete as the captured mercury and other metals are nowpermanently insoluble. The residue 78 may be highly concentrated withheavy metals and may require additional testing for disposal or may useas a process addition within a cement mill. Additionally, theparticulates captured by the particulate collection system 40 a, (CKD80) may be used alone or in combination with the residue 78 as one ofthe additional materials inserted into a finish mill in thecement-making process, which is described in further detail below withreference to FIG. 4.

While the systems described above have been installed at certainlocations, it should be appreciated that the systems can be installed atany number of different locations. For example, the system may beinstalled or placed to contact the cement kiln exhaust gas streamupstream or downstream of the raw mill, upstream and/or downstream ofone or more particulate collection systems, or between one or moreexisting ducts associated therewith. Treatment may thus be accomplishedthrough any of a variety of pre-existing ducts, a gas resonance chamber,a dry scrubber, or through other suitable zones, either prior to orafter the one or more particulate collection systems, including thecement kiln baghouse, electrostatic precipitator, or a flue gasdesulfurization scrubber.

In the illustrative embodiments disclosed herein, the spray injectiontiming may be aligned with the operation of the raw mill 28 or may becontinuous dependent upon the needs or goals of the plant to reduceemissions or comply with any applicable regulations. As shown in FIGS. 1and 2, utilizing the injection system prior to the existing particulatecollection system 40 may reduce investment cost and operating cost whencontrasted with a wet scrubber, dry scrubber application or activatedcarbon injection.

It should be appreciated that in one or more of the embodimentsdisclosed herein there is no requirement for a ‘Polishing Baghouse’. Theinjection system may be installed in-line with an existing kiln baghouseand the material collected may simply be segregated during periods whenit is in operation. A separate dust storage and metering system may beincluded to hold the material until it can be put back into the finishmills on a controlled basis. The collected material can successfully beutilized as a process addition within the cement mills without anydanger of releasing the captured mercury. Once the residual material iscaptured in concrete, it should not re-release as it is substantiallypermanently bound in its stable natural form, unlike what generallyresults from the use of activated carbon or sorbent technology. Thecaptured mercury is contained in its stable natural form. It should notre-release into the air or leach into the soil unless it is physicallyprocessed again through a kiln or combustion system.

Any of the embodiments disclosed herein may include a dust storage andmetering system for containment of the captured mCKD and re-introductionof the mCKD to the cement milling process to be used in furtherproduction steps or recycling of the mCKD back into the kiln processafter removal of the entrained heavy metals such as mercury. The mCKDcan be transferred directly to a storage silo for controlled meteringback into a cement grinding mill, as a process addition, and/or useddirectly as a filler material within a concrete batch plant, asphaltplant or landfilled as non-leachable mCKD.

A method of recycling the mCKD and other raw materials according to anillustrative embodiment is described with reference to FIG. 4. A clinker82 produced in the kiln is cooled and may be transferred to a storagesilo 84 for controlled metering into one or more finish mills 86.Additionally, gypsum 88 may be transferred to a storage silo 90 forcontrolled metering into the finish mill 86. The gypsum 88 may be usedas a process addition to the finish mill 86, replacing, for example,about 5.0% of the total raw materials being utilized. In an illustrativeembodiment, the gypsum 88 is a modified synthetic gypsum (mSyngyp)captured by a flue gas desulfurization scrubber.

As illustrated in FIG. 4, a dust storage and metering system forcontainment of the captured mCKD 92 and re-introduction of the mCKD 92to the cement milling process is included. The mCKD 92 can betransferred directly to a storage silo 94 for controlled metering intothe finish mill 86, as a process addition. The mCKD 92 may be used as aprocess addition to a finish mill 86, replacing, for example, up toabout 5.0% of the total raw materials being utilized. It should beappreciated that the mCKD may make up a larger or smaller percentage ofthe total materials as understood by those skilled in the art in view ofthe present disclosure.

The mCKD 92 is ultimately bound within the Portland cement and used asconcrete, with the resultant material being stabilized andnon-leachable. As illustrated in FIG. 4, a dust storage and meteringsystem is used to hold the mCKD 92 until it can be put back into thefinish mill 86 on a controlled basis. As described above, the mCKD 92 issubstantially permanently bound in its stable natural form, as such; thecollected mCKD 92 can successfully be utilized as a process additionwithin the cement mill without any danger of releasing the capturedmercury.

Installation of the mCKD dust storage and metering system may allow theplant to effectively manage the mCKD material 92 and test it in advanceof recycling, re-using or disposing.

In another illustrative embodiment, a continual emission monitoringsystem capable of accurately measuring mercury and other heavy metalsfor monitoring of system performance may be implemented as part of thesystem.

An example of an integrated injection system according to anillustrative embodiment is described with reference to FIGS. 5-13. Withreference to FIG. 5, the integrated injection system is installed in acement plant 96. The plant 96 produces an exhaust gas stream 98 from akiln (not shown), which flows from the kiln downstream through adowncomer duct 102. At the base of the downcomer duct 102 there is adrop out box 104, which is designed to allow any solidified material tofall out of the exhaust gas stream 98, separating it from the gases andparticulate matter that continue through the ductwork. Connected to theoutlet of the drop out box 104 is a duct 106, which carries the exhaustgas stream 98 downstream to a particulate collection system 108. Theexhaust gas stream 98 flows through the particulate collection system108 into a duct 110, which carries the exhaust gas stream 98 downstreamto an exhaust stack 112 through which the exhaust gas stream 98 exitsinto the atmosphere.

Referring to FIGS. 5 and 6, the integrated injection system includes afirst injection point 114 installed in the downcomer duct 102 and asecond injection point 116 installed in the duct 106. The integratedinjection system is located upstream of the particulate collectionsystem 108. As such, and similar to the previously describedembodiments, particulates are captured in the particulate collectionsystem 108 as a dry residual material resulting in modified cement kilndust (mCKD) 118. This mCKD 118 is no longer soluble in terms of leachatein soils, cement or concrete as the captured mercury and other metalsare now permanently insoluble. Again, as in previous versions, the mCKD118 may be used as one of the additional materials inserted into afinish mill in the cement-making process, such as described above withreference to FIG. 4.

A schematic top down view of the first and second injection points 114and 116 according to an illustrative embodiment is described withreference to FIG. 7. As illustrated in FIG. 7, first ports 120 areinstalled in the downcomer duct 102 at the first injection point 114,and second ports 122 are installed in the duct 106 at the secondinjection point 116. As illustrated, the downcomer duct 102 has adiameter of about twenty (20) feet and there are nine (9) first ports120 around the circumference of the downcomer duct 102. The duct 106 hasa diameter of about eleven and a half (11.5) feet and there are nine (9)second ports 122 around the circumference of the duct 106. However, itshould be appreciated that the number of first ports 120 and the numberof second ports 122 may be smaller or larger than nine (9), dependentupon the particular application and sizes of the ducts.

Referring now to FIGS. 7-11, first ports 120 and second ports 122 arefour inches in diameter, and installed at radially spaced locationsaround the circumference of downcomer duct 102 and the duct 106,respectively. The ports are aligned in parallel to each other. Dependingon the particular application, it should be appreciated that the ports120, 122 may be smaller or larger than four inches in diameter, ports120 need not be of the same dimension as ports 122, and the spacing andorientation may be varied. The ports 120, 122 are designed to penetratethe sidewall of the downcomer ducts 102, 106 for insertion of lances 128a-r of spray nozzles into the downcomer ducts 102, 106 as discussedbelow.

In this illustrative embodiment, lances having one or more nozzlespositioned thereon inserted into corresponding ones of the ports 120,122. Each of the ports 120, 122 can hold a lance. However, it should beappreciated that not all of the ports 120, 122 are required to have acorresponding lance inserted therein during operation. The lances mayhave a length that allows the lance to extend from the particular portinto which the lance is received across at least a portion of the duct.It should be appreciated that the lances may have differing lengths andmay extend varying distances across the duct. For example, the lancesmay extend substantially across the duct from corresponding ports, ormay be sized or otherwise configured to extend a portion of the wayacross the duct from such ports.

As seen in FIGS. 7, 9, and 11, cross supports 132 and 136, fitted withsaddles for each lance (not shown), may extend below and across thelances of a corresponding duct and engage the underside or topside ofsuch lances to support them. The cross supports 132 and 136 extend at anangle (perpendicular in this version) to corresponding lances and ismounted through corresponding ports 124, 126.

An embodiment of one of lances 128 a-r according to an illustrativeembodiment is further described with reference to FIG. 8. As illustratedin FIG. 8, a lance 128, such as one of lances 128 a-r described below,has one or more nozzles 130 installed thereon. In this embodiment thelance 128 is made of stainless steel. However, it should be appreciatedthat the lance 128 may be made of other materials, such as but notlimited to iron, aluminum, polymers, and other materials of the type. Inthis embodiment, the nozzles 130 are configured to disperse droplets ofthe treating fluid. The droplet size should be large enough to allow thedroplets to exist long enough and react with the metal(s), such as ionicand elemental mercury, within the exhaust gas stream. In thisembodiment, the droplets may have an average size of about 20-40microns, and more particularly an average size of about 30-40 microns.The droplet size of about 30-40 microns is designed allow the dropletsto reside in the exhaust gas stream for a minimum of about 1-2 secondswhen the temperature at the injection point is on average about 350° F.However, the droplet sizes can be made to vary, for example the dropletsmay have an average size of about 20 microns or larger, dependent uponthe exhaust gas temperature, treating fluid concentration, waterpressure, actual cubic feet per minute, particulate dust load andmercury concentrations, and other factors. For example, it should beappreciated that a higher temperature may be associated with a largerdroplet size, such as about 70 to 90 microns (though this is not anupper limit on suitable droplet size), and a lower temperature may allowfor a smaller droplet size to be used.

A schematic view of a spray pattern through the nozzles 130 within thedowncomer duct 102 at injection point 114 is illustrated and describedwith reference to FIG. 9. As illustrated in FIG. 9, there are nine (9)lances 128 a-i, equally spaced, each having one or more nozzles 130 (asindicated by the circular patterns) and inserted into nine of the firstports 120. In this embodiment, the lances 128 a-i are supported by thecross support 132 that extends between ports 124. The cross support 132may be fitted with saddles for the lances 128 a-i to support the lances128 a-i as the lances 128 a-i extend across the duct 102.

As illustrated in FIG. 9, the nozzles 130 (as indicated by the circularpatterns) have a cone-shaped spray pattern with a round shaped impactarea. However, it should be appreciated that nozzles having differingshaped spray patterns and impact areas may be used.

In this embodiment, the lances 128 a and 128 i each have one (1) nozzle130, the lances 128 b and 128 h each have four (4) nozzles 130, thelances 128 a, 128 c, and 128 g each have five (5) nozzles 130, and thelances 128 d and 128 f each have six (6) nozzles 130. The spraypatterns, illustrated by the circular patterns, of the nozzles 130 coverabout 90% of the total cross sectional area of the downcomer duct 102.However, it should be appreciated that a different arrangement or numberof nozzles, smaller, larger, or different spray patterns may be used,and that the amount of coverage of the total cross sectional area of thedowncomer duct 102 may be varied so as to be a higher or smallerpercentage.

Similarly, a schematic view of a spray pattern through the nozzles 130within the duct 106 at injection point 116 is illustrated and describedwith reference to FIG. 11. As illustrated in FIG. 11, there are nine (9)lances 128 j-r, equally spaced, each having one or more nozzles 130 (asindicated by the circular patterns) and inserted into nine of the secondports 122. In this embodiment, the lances 128 j-r are supported by thecross support 136 that extends between ports 126. The cross support 136may be fitted with saddles for the lances 128 j-r to support the lances128 j-r as the lances 128 j-r extend across the duct 106.

As illustrated in FIG. 11, the nozzles 130 (as indicated by the circularpatterns) have a cone-shaped spray pattern with a round shaped impactarea. However, it should be appreciated that nozzles having differingshaped spray patterns and impact areas may be used.

In this embodiment, the lances 128 j and 128 r each have one (1) nozzle130, the lances 128 k-m and 128 o-q each have four (4) nozzles 130, andthe lance 128 n has five (5) nozzles 130. The spray patterns,illustrated by the circular patterns, of the nozzles 130 cover about 90%of the total cross sectional area of the duct 106. However, it should beappreciated that any number of nozzles having smaller or larger spraypatterns may be used to cover a higher or smaller percentage of thetotal cross sectional area of the duct 106.

As illustrated, with reference to FIGS. 8-10, the nozzles 130 arefluidly connected to one or more vessels for storing the treating fluid,via one or more of the lances 128 a-i, through one or more fluidconnections 134, such as pipes and/or hoses. The treating fluid isstored in the vessel and transported (for example via a pump) throughthe fluid connections 134, through the one or more lances 128 a-i andexits through the nozzles 130 within the downcomer duct 102. Thetreating fluid then contacts the cement kiln exhaust gas stream 98within the downcomer duct 102. Similarly, as illustrated with referenceto FIGS. 8, 11, and 12, the nozzles 130 on the lances 128 j-r at thesecond injection point 116 in the duct 106 are fluidly connected to avessel, containing the treating fluid, via one or more fluid connections138, such as pipes and/or hoses.

The integrated injection system, described above with reference to FIGS.5-12, can be implemented in cement plant 96 (FIG. 5) to remove mercuryfrom exhaust gas stream 98. The temperature of the exhaust gas stream 98varies dependent upon operation of an inline raw mill and/or the kilnconditions. In this illustrative embodiment, the temperature at theinlet to the downcomer duct 102, which is upstream of the raw mill,varies from about 600 to 800° F. Temperatures at the inlet to theparticulate collection system 108 typically range from about 240-300° F.to protect the particulate collection system 108. When the raw mill isoperating, the exhaust gas stream 98 loses heat as it passes through theraw mill to dry out the raw materials while grinding is taking place.When the raw mill is not operating, it is generally necessary to lowerthe temperature of the exhaust gas stream 98 by using a high pressurewater spray in the downcomer duct 102. This typically cools the exhaustgas stream 98 down to about 325-395° F. at the inlet to the particulatecollection system 108 to protect the particulate collection system 108.

The particulate loading of exhaust gas stream 98 can be as high as 20tons per hour (tph) through the downcomer duct 102 and is not dependenton raw mill operation. The exhaust gas stream 98 gas volume can vary by4,000,000 standard cubic feet per hour (scfh) during operation due totemperature fluctuations and process conditions.

In this embodiment, the treating fluid contains a reagent and water. Thereagent is 30% calcium polysulfide in water. The reagent and water isinjected in a ratio of about 1:4 when the raw mill is off and thetemperature is reduced to about 350° F. at the exit of the duct 106. Asdescribed above, the first injection point 114 is installed in thedowncomer duct 102, prior to the drop out box 104, and the secondinjection point is installed in the duct 106, after the drop out box104. The treating fluid is injected through the nozzles 130 at a rate ofabout fifteen (15) gallons per minute, a pressure of about 45 psi, andhas an average droplet size of about 30-40 microns. The droplet size ofabout 30-40 microns is designed to allow the reagent to reside in theexhaust gas stream 98 long enough to come into contact with and reactwith the ionic and elemental mercury within the exhaust gas stream 98 toform mercury sulfide. In this embodiment, the 30-40 micron dropletsreside for a minimum of about 1-2 seconds within the exhaust gas stream98 having a temperature of about 350° F., on average, beforeevaporating. Additionally, the 30-40 micron droplets prevent the reagentfrom building up on a downstream preheater ID fan (not shown) that ispresent in the cement plant 96. Under these conditions, a smallerdroplet may not provide the droplet enough life to allow the reaction tooccur, and a larger droplet may carry to the preheater ID fan where itmay contribute to buildup and vibration leading to fan failure.

A table of exemplary injection runs and corresponding results isillustrated and described with reference to FIGS. 5 and 13. Asillustrated in FIG. 13, six runs were conducted. The amount of mercurythat was captured through use of the integrated injection system wascalculated based on measurements taken at a first measurement point 140located prior to the first injection point 114 and a second measurementpoint 142 located prior to the inlet of the particulate collectionsystem 108, as illustrated in FIG. 5.

During runs 1 and 2, the treating fluid was not injected and the amountof mercury present in the exhaust gas stream 98 at the secondmeasurement point was 512.6 ug/m and 532.3 ug/m, respectively. Duringruns 3 and 4, the treating fluid was injected at only one of theinjection points, namely the first injection point 114. The treatingfluid was the reagent water mixture containing the reagent and the waterin a ratio of about 1:4. The treating fluid was injected at only one ofthe injection points, the first injection point 114 at a rate of aboutfifteen (15) gallons per minute (GPM) for about thirty (30) minutes. Thetreating fluid was injected on a continual basis allowing the reagent tointercept the exhaust gas stream 98 for a minimum of about 1-2 seconds,during which the reaction occurs. The average total amount of mercury(i.e. the amount in the particulate and vapor) in the exhaust gas stream98 at the first measurement point 140 (before any treatment) wasdetermined to be about 480 ug/m during runs 3 and 4. The average totalamount of mercury in the exhaust gas stream 98 at the second measurementpoint 142 (after treatment) was determined to be about 281.8 ug/m 3 andabout 326.6 ug/m 3 during runs 3 and 4, respectively. When comparingmercury levels before and after treatment at a single location along thepath of the exhaust gases, during the same runs, run 3 achieved acapture rate of about 41.3% of the total mercury in the exhaust gasstream 98, and run 4 achieved a capture rate of about 32% of the totalmercury in the exhaust gas stream 98. Thus, injection of the treatingfluid at the first injection point 114 was measured to achieve anaverage capture rate of about 36.7% of the total mercury in the exhaustgas stream 98 across runs 3 and 4.

The mercury capture rate is even higher when comparing the untreatedexhaust gas stream at the second measurement point 142 from runs 1 and 2to the treated stream at the same measurement point 142 from runs 3 and4. Specifically, average total mercury at the second measurement point142 in runs 1 and 2 was 522 ug/m and in runs 3 and 4 was 304 ug/m,representing a capture rate of about 42%.

During runs 5 and 6, the treating fluid was injected through both thefirst injection point 114 and the second injection point 116. Thetreating fluid was the reagent water mixture containing the reagent andthe water in a ratio of about 1:4. The treating fluid was injected at arate of about fifteen (15) gallons per minute (GPM) for about fifteen(15) minutes through both injection points 114 and 116. The treatingfluid was injected through both injection points 114 and 116 on acontinual basis allowing the reagent to intercept the exhaust gas stream98 for a minimum of about 1-2 seconds at each point, during which thetreatment occurs. The average total amount of mercury (i.e. the amountin the particulate and vapor phase) in the exhaust gas stream 98 at thefirst measurement point 140 was determined to be about 497 ug/m and 475ug/m during runs 5 and 6, respectively. The average total amount ofmercury in the exhaust gas stream 98 at the second measurement point 142was determined to be about 203.5 ug/m and about 223.3 ug/m during runs 5and 6, respectively. Run 5 achieved a capture rate of about 59% of thetotal mercury in the exhaust gas stream 98, and run 6 achieved a capturerate of about 52.9% of the total mercury in the exhaust gas stream 98.Thus, injection of the treating fluid at both of the injection points114 and 116 can achieve a capture rate of about 56% of the total mercuryand a capture rate of about 66% of the amount of mercury in the vapor ofthe exhaust gas stream 98.

Again, the mercury capture rate is even higher when comparing theexhaust gas treated in runs 5 and 6 at measurement point 142 to theuntreated exhaust gas from runs 1 and 2, all of which involved about thesame rate of kiln feed. Specifically, average total mercury at point 142in untreated runs 1 and 2 was 522 ug/m, compared to average totalmercury of 213 ug/m in runs 5 and 6, representing a capture rate ofabout 59% of the total mercury.

In the runs described above, treatment by the integrated injectionsystem illustrated in FIGS. 5-12, occurs prior to the exhaust gas stream98 entering the particulate collection system 108. The treating fluidwas injected on a continual basis allowing the reagent to intercept theexhaust gas stream 98, for a minimum of about 1-2 seconds, during whichthe reaction occurs. During the reaction, the reagent interacts withelemental and ionic mercury in the exhaust gas stream 98 converting theelemental and ionic mercury into mercury sulfide. As such, theparticulates (including mercury sulfide) are carried into theparticulate collection system 108. The particulates are captured as adry residual material resulting in the modified cement kiln dust (mCKD)118, as illustrated in FIG. 5. The mCKD 118 may no longer be soluble interms of leachate in soils, cement or concrete as the captured mercuryand other metals are now permanently insoluble. The mCKD 118 may be usedas one of the additional materials inserted into a finish mill in thecement-making process, such as described above with reference to FIG. 4.

Although the runs described above were conducted with the raw mill off,it should be appreciated that the systems and methods described hereincan be utilized to remove mercury and other metal(s) when the raw millis on, or under any number of other operating protocols. When the rawmill is off, the mercury content is generally expected to be higher thanwhen the raw mill is on. Thus, it is expected that the above-describedtreating fluid processes will cause an even larger percentage of mercuryto be removed from the exhaust gas stream when the raw mill is on.

While the systems and methods disclosed herein are described withreference to certain embodiments, it should be appreciated that cementkiln configurations may vary greatly and thus locations andconfigurations of the treatment system relative to the kiln exhaust gasstream may be correspondingly varied to suit the particular cement kiln.It should also be appreciated that any of the embodiments contemplatedherein may or may not require one or more secondary particulate removalsystems, depending on the particular applications.

Depending on the individual kiln operation, raw materials, and fuels,the systems disclosed herein may run only intermittently, on an asneeded basis, or they may run substantially continually to achievedesired reduction goals, including the injection of treating fluid 100%of the time. In most cases, the highest period of mercury emissionrelates to when the in-line vertical mill or raw mill is off or whenthere is a temperature discrepancy in the kiln baghouse, ESP, or otherparticulate collection system. Accordingly, the treatment process may beconfigured to run during such off-line periods, or it may be triggeredto run in response to any number of parameters, such as time, theexceeding of certain emission thresholds, running emission averages,measurements of gas constituents, and other parameters of the type. Eachsystem may be tailored to each cement kiln based on actual emissionmodeling, raw materials, costs, and any number of other operational,emission, or functional parameters.

In an illustrative embodiment, the duct(s), chambers, or other treatmentzones associated with the treatment system are configured to addresstemperature drops as the exhaust stream travels downstream. For example,as disclosed above, in certain embodiments, the treatment zone (duct,chamber, cyclone, etc.) may be selected or configured so that the inlettemperature of the treatment zone is hot enough to accommodate thetemperature drop across the zone while in operation, while meeting theoperational requirements of a downstream baghouse, ESP, or otherparticulate collection system. Such an inlet temperature avoids bothhigh heat situations and low dew point situations which lead tocorrosion.

The systems, methods, and processes disclosed herein have beenidentified, adapted to, and designed for the cement industry. In oneform, the systems, methods, and processes disclosed herein may provide alower capital cost, lower operating cost, and most importantly reducedmercury emission levels.

It should be appreciated that a version of this technology can also beapplied to cement-making plants equipped with a wet scrubber or alreadydesigned for use of activated carbon injection. Retrofitting of existingfacilities is expressly among the possible configurations.

It should also be understood that, using the systems and methodsdisclosed herein, mercury is captured regardless of where it isgenerated during the cement-making process, without the need forre-heating. The systems and methods disclosed herein may allow thecement plants to use a greater variety of raw materials without fear ofexceeding any applicable emission limits for mercury or other heavymetals captured as described in this disclosure. Depending on the volumeof residual material generated, the portion which cannot be utilized asa process addition will have to be disposed of, but this is expected tobe a minor volume in the overall context.

While the above description relates generally to mercury capture, itshould be appreciated that the systems, methods, processes, andtechnology disclosed herein may be modified to capture hexavalentchromium and a variety of other metals and emission hot points.

The matter set forth in the foregoing description and accompanyingdrawings is offered by way of illustration only and not as a limitation.While the systems, methods, and apparatuses for cement kiln exhaust gaspollution reduction have been described and illustrated in connectionwith certain embodiments, many variations and modifications will beevident to those skilled in the art and may be made without departingfrom the spirit and scope of the disclosure. The disclosure is thus notto be limited to the precise details of methodology or construction setforth above as such variations and modification are intended to beincluded within the scope of the disclosure.

What is claimed is:
 1. A method for reducing pollution in a cement kilnenvironment comprising: treating a cement kiln exhaust gas stream with atreating fluid comprising a reagent containing a water solublealkaline-earth metal sulfide by injecting said treating fluid into saidcement kiln exhaust gas stream prior to a particulate collection system.2. The method of claim 1, wherein said injecting further comprisesspraying droplets of said treating fluid into said cement kiln exhaustgas stream.
 3. The method of claim 1, wherein said treating furthercomprises injecting said treating fluid into said cement kiln exhaustgas stream at a point where said cement kiln exhaust gas stream has atemperature of about 350 degrees Fahrenheit.
 4. The method of claim 1,wherein said treating further comprises injecting said treating fluidinto said cement kiln exhaust gas stream subsequent to a firstparticulate collection system and prior to a second particulatecollection system.
 5. The method of claim 1, wherein said treatingfurther comprises injecting said treating fluid into a gas resonancechamber carrying said cement kiln exhaust gas stream.
 6. The method ofclaim 1, wherein said treating further comprises injecting said treatingfluid into a duct carrying said cement kiln exhaust gas stream.
 7. Themethod of claim 2, wherein said spraying said droplets further includesspraying said droplets having a size configured to allow said dropletsto have a minimum residence time of about 1 second to about 4 seconds.8. The method of claim 2, wherein said spraying said droplets furtherincludes spraying said droplets having a size configured to allow saiddroplets to have a minimum residence time of about 1 second to about 2seconds.
 9. The method of claim 2, wherein said spraying said dropletsfurther includes spraying said droplets having an average size of atleast about 20 microns.
 10. The method of claim 2, wherein said sprayingsaid droplets further includes spraying said droplets having an averagesize of about 30 microns to about 40 microns.
 11. A system for treatingcement kiln exhaust gas comprising: a treating fluid comprising: areagent containing a water soluble alkaline-earth metal sulfide inwater; and at least one nozzle configured to communicate with a cementkiln exhaust gas stream from a kiln, said at least one nozzle configuredto spray droplets of said treating fluid into said cement kiln exhaustgas stream.
 12. The system of claim 11, wherein said treating fluidfurther comprises at least one of a surfactant, a dispersant, and ahyperdispersant.
 13. The system of claim 11, wherein said at least onenozzle is configured to spray said droplets having a size configured toallow said droplets to have a minimum residence time of about 1 secondto about 4 seconds.
 14. The system of claim 13, wherein said at leastone nozzle is configured to spray said droplets having an average sizeof at least about 20 microns.
 15. The method of claim 1, wherein thealkaline-earth metal sulfide comprises an alkaline-earth metalpolysulfide.
 16. The system of claim 11, wherein the alkaline-earthmetal sulfide comprises an alkaline-earth metal polysulfide.